1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device, a method for fabricating the same, and a method for operating the same.
2. Description of the Related Art
A nonvolatile memory device is a memory device in which stored data are maintained as they are even though power supply is interrupted. Currently, various nonvolatile memory devices such as a NAND type flash memory are widely used.
FIG. 1 is a circuit diagram showing a conventional nonvolatile memory device.
Referring to FIG. 1, a conventional nonvolatile memory device includes a plurality of bit lines BL which extend in a column direction and are arranged parallel to one another and a source line SL which extends in a row direction. The bit lines BL include even bit lines BLe and odd bit lines BLo which are alternately arranged.
A string, in which a drain selection transistor DST, a plurality of memory transistors MT, and a source selection transistor SST are connected in series, is disposed between each bit line BL and the source line SL.
A drain selection line DSL is connected to the gate electrodes of drain selection transistors DST and extends in the row direction. Word lines WL are connected to the control gate electrodes of memory transistors MT and extend in the row direction. A source selection line SSL is connected to the gate electrodes of source selection transistors SST and extends in the row direction.
In the nonvolatile memory device configured as described above, a data program operation and a data read operation are performed on every page as a unit. In particular, an even page program operation for programming a certain cell of the string connected to the even bit line BLe and an odd page program operation for programming a certain cell of the string connected to the odd bit line BLo are separately performed. Even page read and odd page read operations are applied in the same manner.
However, the conventional nonvolatile memory device has the following features.
In the conventional nonvolatile memory device, since the bit lines BL and the source line SL extend in different directions, they may not be disposed on the same layer. That is to say, the bit lines BL and the source line SL are to be formed as different layers through different processes. In this case, since mask processes and etching processes are to be separately performed in order to form the bit lines BL and the source line SL, processes become complicated.
Also, in the conventional nonvolatile memory device, the source line SL is connected to all strings in common. Accordingly, in a read operation, the way of sensing voltage changes in the respective bit lines BL is to be used. However, in this case, sensing noise may increase.